My childhood home was bizarre. Built along a hillside, it had nine different levels, four large staircases, two or three smaller ones, and a ladder to a finished loft. It didn’t have any truly secret rooms, but all the unused attic space was accessed from the side via doors. Two in the loft, one in the master bedroom, and one in my bedroom.
Inside my attic space which we called my “back room,” was a tiny door that opened to a small crawl space. I probably should have been frightened by it, but there was literally nothing in there. When I visited the house recently, the family we sold it to were still there and let me show my wife around. The woman didn’t know about the tiny second door.
There was also a small cellar, it’s door tucked away in the corner of the living room. A piano or cabinet hid it easily.
Also a fireplace open to two rooms on either side, a built-in vacuum system you could talk to other rooms through… that house had character.